Numerous semiconductor structures are produced by the attachment of two or more elements to one another to produce a desired structure. Such attachment methods may be utilized when the elements comprising the desired structure may not be readily fabricated by conventional means such as, for example, direct growth or deposition.
The attachment of two or more elements is commonly performed utilizing bonding techniques. Such bonding techniques encompass a number of methods commonly referred to as, for example, molecular, fusion, metallic, adhesive, solder and direct bonding. For example, see the journal publications of Tong et al., Materials, Chemistry and Physics 37:101 (1994), entitled “Semiconductor Wafer Bonding: Recent Developments,” and Christiansen et al., Proceedings of the IEEE 94 12 2060, 2006, entitled “Wafer Direct Bonding: From Advanced Substrate Engineering to Future Applications in Micro/Nanoelectronics.”
The bonding of elements to one another is commonly assisted by the formation of a bonding layer on a surface of at least one of the elements. The surface chemistry of the bonding layer can improve the adhesion of the two elements to one another, such that the two elements can be attached with sufficient bonding energy to enable further processing to be performed on the bonded semiconductor structure without unwanted premature separation.
Bonding layers may encompass a multitude of materials including, for example, conductors (e.g., metals), semiconductors and insulators. One of the more common bonding layers comprises a silicate such as, for example, silicon dioxide, wherein the surface chemistry of the silicon dioxide surface may comprise silanol (Si—OH) groups capable of producing high bonding energies. However, the use of insulating bonding layers may prevent the flow of electrons between the bonded elements, which may impede or prevent electrical conductivity between the two or more elements.
The flow of electrons and, hence, electrical current between two bonding elements can be realized by utilizing metallic bonding layers. Metallic bonding layers have been produced using a number of different metallic materials such as, for example, copper and gold. However, the use of metallic bonding layers can severely limit the transmission of light through the bonded structure since metallic bonding layers may substantially prevent light transmission when the metallic layers are above a certain thickness. Therefore, metallic bonding layers may not be suitable or ideal bonding materials when bonding elements through which light may be transmitted during use, such as those used in optical, optoelectronic or photovoltaic structures.